Drive unit, preferably for lifting columns for height-adjustable tables, and a lifting column

ABSTRACT

A drive device, preferably for lifting columns for height-adjustable tables, comprising an endless chain ( 31 ) running over first and second chain wheels ( 16, 17 ) with a first chain run and a second chain run between the two chain wheels, wherein at least one chain run may be connected with a movable element in the structure in which the drive device is incorporated. The drive device comprises a stick-shaped element ( 5 ), where the chain wheels ( 16, 17 ) are mounted at their respective ends and the one chain wheel ( 16 ) is driven by an electric motor ( 6 ) via a transmission and where both the electric motor and the transmission are likewise mounted on the stick-shaped element so that the drive device essentially appears as a finished, mountable unit. The length of stroke is determined solely by the selection of the length of the drive device, just as the drive device may be constructed for a slender column profile. The drive device is moreover easy to mount.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a drive device, preferably for liftingcolumns for height-adjustable tables, and comprising an endless chainrunning over first and second chain wheels with a first chain run and asecond chain run between the two chain wheels, wherein at least onechain run may be connected with a movable element in the structure inwhich the drive device is to be incorporated. The invention moreoverrelates to a lifting column containing such a drive device.

2. The Prior Art

SE 513 249, MPI Teknik AB, discloses a lifting column having threemembers whose movement is based on an endless chain in a closed tubularprofile. Two rods protruding from the respective ends of the tubularprofile are secured to the chain. The two rods are secured to the outermember and the inner member, respectively, of the column, while theclosed tubular profile with the chain is secured in the central member.The telescopic movement of the column is caused by a linear actuator,which is secured with its one end to a base plate in the outer memberand to the top of the tubular profile with the chain. The structureperforms well as far as it goes, but it requires a column of aconsiderable cross-section to accommodate the actuator and the tubularmember with the chain arranged side by side. In addition, the movementof the column is limited to the length of stroke of the actuator. If agreat travel is desired in the column, it requires an actuator having agreat length of stroke, but then the mounting height of the columnbecomes large, as the length of stroke of the actuator is directlyrelated to its length—great length of stroke, long actuator. Thestructure is not particularly easy to mount either, just as the courseof force is not optimum, resulting in inexpedient moment loads.

The object of the invention is to obviate the problems outlined above.

SUMMARY OF THE INVENTION

This achieved according to the invention by a drive device of the typestated in the opening paragraph, configured as a stick-shaped element,wherein the chain wheels are mounted at respective ends, and wherein theone chain wheel is driven by an electric motor via a transmission, andwherein both the electric motor and the transmission are likewisemounted on the stick-shaped element such that the drive deviceessentially appears as a finished, mountable unit. The length of strokeis determined solely by the selection of the length of the drive deviceand is not tied to the length of stroke of an actuator, just as thedrive device may be configured for a slender column profile and be madeeasy to mount.

The stick-shaped element may be made in two halves which may beassembled about a longitudinal plane, recesses being provided in twoparts for various elements. In another embodiment, the stick-shapedelement is an entity in which recesses are provided in an area up to themotor for the transmission or a part thereof as well as for the onechain wheel, which recesses may preferably be closed by a cover shield.The stick-shaped element may be moulded of plastics as well as of metal.

In an embodiment, at least the chain wheel most remote from the motor ismounted on a subelement of the stick-shaped element and is secured to itlongitudinally slidably. This involves mounting advantages when mountingthe chain, and it also allows an accurate chain tightening, just as itmay be subsequently adjusted.

In an embodiment, the transmission is based on a planetary gear having atoothed rim with an internal toothing in engagement with a planet wheel,which is in turn in engagement with a sun wheel, said toothed rim beingconfigured as the one chain wheel. This gives an extremely compactstructure as well as a great gearing. The planetary gear has theadditional advantage that it is relatively easy to integrate in thestick-shaped element. Expediently, the transmission further comprises aworm drive, where the motor shaft is formed with the worm. This is alsorelatively easy to arrange in the stick-shaped element. With atransmission consisting of a worm drive and a planetary gear it ispossible to achieve a great gearing, which is expedient when usingmotors having a large number of revolutions.

In an embodiment, the worm drive and the planetary gear are connectedwith a chain drive, wherein the worm wheel is connected with a firstchain wheel and the sun wheel with a second chain wheel. The chain driveis flat and may therefore also be incorporated relatively easily in thestick-shaped element at the side of the planetary gear and the wormdrive.

A specially constructed chain tightener for the chain drive comprises atleast a spring-loaded block, one end of the block being intended forengagement with the chain, the other end having a snap locking partintended for cooperation with a boss for retention of the block againstthe spring action. When the chain is mounted, the snap lock is releasedand the block is engaged with the chain by the spring force to tightenit. This is simple and allows easy mounting. Expediently, there is achain tightener for each chain run, preferably arranged inwardly of thechain, thereby allowing the same boss to be used for holding the blocks.

In an embodiment, the electrical wire(s) is typically a wire havingseveral conductors to the drive unit connected with the one rod. Thisensures that the wire does not get jammed in operation. To guide thewire additionally, the stick-shaped element may be formed with a cavityon the side for receiving the length of the wire in excess at any time,depending on the extended position of the drive unit.

In an embodiment, the end stop positions are determined by two end stopswitches, preferably mounted on a common printed circuit board which maybe inserted into a slot in the rod. The rods may be utilized foractivating the end stop switches, e.g. in that the rods are providedwith means or constructed themselves for activation of the end stopswitches. It will be appreciated that the chain may also be used foractivation of the end stop switches, but the rods are preferred sincethey are free or essentially free of grease and their length iswell-defined, whereas the chain may be stretched.

In an expedient embodiment, the rods have a U-shaped cross-sectionwhich, with the sides, extends down around the chain. This provides agood control of the rods particularly during mounting, and the U-shapesimultaneously gives a good strength and rigidity.

The side of one of the rods may be formed with a longitudinal incisionfor the function key of the end stop switches so that in the positionsbetween the end stops the function keys protrude into the incision,while at the end stops the side of the rail will activate the respectiveend stop switch, which is a simple, safe and distinct way of activatingthe end stop switches.

In an embodiment, a guide for the respective rod is arranged on each endof the stick-shaped element, which has advantages in terms of mountingand transport, but it is also an advantage in terms of strength sincethe guide prevents the rods from deflecting, as they are subjected tocolumn loads. The rods may additionally be guided laterally by a flangeon the stick-shaped element which extends into the cavity of theU-shaped rods. The rods are expediently riveted to a U-shaped link ofthe chain, which is simple and inexpensive.

For attachment in the structure in which the drive device is to beincorporated, the outer end of the rods may be formed with flaps whichare inserted into corresponding slots and are bent or twisted. WithU-shaped rods, the two sides or the back may form the basis for theprovision of flaps.

A simple mounting of the motor on the stick-shaped element is achievedby a dovetail connection, said motor being preferably provided with afront cover formed with a dovetail groove and a counterpart in thestick-shaped element.

In an embodiment, at least one end of the stick-shaped element isprovided with at least a boss on each side as a lateral guide in thestructure in which the drive device is to be incorporated. It is evidentthat the structure in which the drive unit is to be incorporated may beformed with corresponding means for fixing the drive unit.

The drive device may also be provided with a rotary potentiometer forabsolute positional determination of the extended position of the drivedevice, said potentiometer being preferably arranged in a recess in thestick-shaped element and drawn via a toothed wheel on its shaft and inengagement with the drive chain, which is simple and functional. It willbe appreciated, however, that other solutions may be used, such asoptical and magnetic encoders, Hall sensors, etc.

As stated initially, the invention also relates to a lifting columnhaving at least two, preferably three, mutually telescopically slidablemembers equipped with a drive Las stated in claims 1–2 of the invention.The lifting column may be configured as a table leg forheight-adjustable tables. It will be appreciated that the drive devicemay also be used as a linear actuator.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained more fully below with reference to theaccompanying drawings. In the drawing:

FIG. 1 shows a lifting column having three members,

FIG. 2 shows the drive device in the lifting column of FIG. 1,

FIG. 3 shows a first longitudinal section of the lifting column of FIG.1,

FIG. 4 shows a second longitudinal section of the lifting column of FIG.1,

FIG. 5 shows a cross-section 5—5 of the column as shown in FIG. 3,

FIG. 6 shows a cross-section 6—6 of the column as shown in FIG. 3,

FIG. 7 shows a modified embodiment of a drive device useful in a liftingcolumn, seen from one side,

FIG. 8 shows the same as FIG. 7, seen from the other side, and

FIG. 9 shows the drive device of FIG. 7 in an extended position.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The column shown in the drawings consists of three members, viz, anouter profile 1, an intermediate profile 2 and an inner profile 3.

A drive device 4 as shown in FIG. 2 is mounted in the intermediateprofile 2. This drive device is based on a stick-shaped element 5consisting of two plastic shells 5 a, 5 b.

A DC motor 6 is secured to one end of the stick-shaped element 5, withan extension of the motor shaft constructed as a worm 7. Thestick-shaped element mounts a shaft with a worm wheel 8 driven by theworm. A screw spring 9 is mounted on a cylindrical part of the wormwheel, said screw spring serving as a load moment barrier, cf. WO98/30816, Linak A/S, see the spring and coupling parts positions 20–22in the document.

A toothed wheel 10 for a drive chain 24 (shown in FIG. 7), which drivesa planetary gear 11, is mounted on the same shaft as the worm wheel.

The planetary gear 11 with its such wheel 12 planet wheels 13 andinternally toothed rim 14 is mounted in the stick-shaped element 5,i.e., the stick shaped element is locally formed as a housing for theplanetary gear. A chain wheel 15 for the drive chain is mounted on theshaft of the sun wheel 12. The stick-shaped element is constructed suchthat the tooth rim slides on the plastics, so that the planet wheel justtransfers moments and not lateral forces. The sun wheel is sintered andmerges into a spline. The transition between the toothing and the splineis stepped in an inclined shoulder, there being inwardly provided abushing which in turn carries a bearing. The use of the bushing allowsthe spline.

The toothed rim 14 is externally constructed as a chain wheel 16. It maybe configured as a unit, e.g., in sintered metal, or joined as twoindependent units. A chain wheel 17 of a dimension similar to the chainwheel 16 is mounted at the other end of the stick-shaped element 5. Achain 31 (shown in FIGS. 8 and 9) runs around these two chain wheels 16,17 and forms two parallel chain runs between the two chain wheels.

A rod 18 is mounted with its one end on the one chain run at the chainwheel 16, the other end of said rod being secured to the outer profile 1via an end plate 20. A corresponding rod 21 is mounted on the otherchain run at the chain wheel 17, but extends in the opposite directionand is secured with the other end to the inner profile 3 via an endplate 22. When the motor is activated, the two rods 18, 21, because ofthe movement of the chain, will extend the outer profile 1 and the innerprofile 3, respectively, synchronously relative to the intermediateprofile 2, and correspondingly retract them when the rotation of themotor is reversed.

The chain wheel 17 is mounted on a separate subelement 23 of thestick-shaped element. This subelement has a stem 23 a, whereby it isreceived in a cavity at the end of the stick-shaped element. The end ofthe stem is inclined and cooperates with a wedge at the bottom of thecavity. The wedge may be adjusted to and fro by a screw for longitudinaldisplacement of the element 23 and thereby adjustment of the tighteningof the chain.

With the transmission sequence: worm drive 7, 8, chain drive 10, 15 andplanetary gear 11 as well as toothed wheel 16 externally on the toothedrim 14 of the planetary gear, a great reduction in the transmission isachieved. It is a further advantage that the gearing may easily beadjusted for current needs by changing the chain wheels 10, 15 of thechain drive.

The column has a relatively short mounting height as the motor isarranged in the area of the necessary overlap between the inner profile3 and the intermediate profile 2. The specially constructed planetarygear 11 also contributes to reducing the mounting dimension.

As will appear, the mounting of the drive device is simple, as thevarious parts are mounted in one half of the stick-shaped element 5 andare subsequently closed by the other half, and finally the chain istightened. The drive device is hereby ready for mounting in a column.

FIG. 7 of the drawing shows a modified embodiment of the drive device,in which the same reference numerals are used as in the foregoing. Inthe modified embodiment, the stick-shaped element 5 is formed by asingle element, and the housing for the planetary gear 11 and the otherparts mounted in the stick-shaped element is formed by a space, which issubsequently closed by a cover 25. Provision has also been made for themounting of a rotary potentiometer 26, if it is desired to have anabsolute positional determination of the extended position of the drivedevice. The potentiometer is driven via a toothed wheel on the shaft 27and is in engagement with the drive chain 24. Of course, other forms ofpositional determinations may be used, e.g. Hall sensors.

The end stop positions may be determined by two end stop switches 28, 29mounted on a printed circuit board 30 which is inserted into a slot inthe rod. The rods 18, 21 have a U-shaped cross-section which, with thesides, extends down around the chain 31. The side of the rod 21 isformed with a longitudinal incision for the keys of the end stopswitches 28, 29. In the positions between the end stops the keys extendinto the incision, but at the end stops the side of the rail willactivate the respective end stop switch. Alternatively, the inner sideof the rail might be equipped with a member for activation of the endstop switches.

Wiring for the motor and the end stop switches is introduced at the topof the column. It is typically a wire having at least four or fiveconductors. Since the motor and the end stop switches are positioned inthe central member, the wire must have a freely movable excess length atleast corresponding to the distance which the inner member may beextended. To avoid damage to the wire or the structure, the wire issecured to the rod 21 by means of wire holders 32. The wire is run witha curve into a chamber 33 in the stick-shaped element. This chamber isformed between the side of the stick-shaped element and a cover 34 andis open toward the rod 21 along the entire longitudinal side. In theretracted state, the wire extends from the cable holder 32′ in a curveinto the chamber at 33 and extends at the internal longitudinal side inthe chamber up to the motor and the printed circuit board with the endstop switches. When the drive device is extended, the wire will bepulled along out through the side of the chamber 33. The wire is therebycontrolled so that it is not damaged or does not cause operationaldisturbances by getting caught in the drive device or the column.

The outer end of the stick-shaped element has a guide 35 for the rod 18,and for the rod 21 there is a guide 36 which merely keeps the rodagainst the drive device. The rod 21 is guided in the lateral directionby a flange 37 on the stick-shaped element.

A special chain tightener is provided to prevent noise from the drivechain 24. The chain tightener comprises two blocks 38, where one end isintended for engagement with the chain, while the other end has afin-shaped snap locking part intended for insertion into a slot in anupright boss 39. Only one block is shown in the drawing. The blocks arespring-loaded by a small spring for engagement with the chain. Prior tomounting, the two blocks are kept back on the boss 39. When the drivechain is mounted, the blocks are released for engagement with it. Thisfacilitates the mounting and also ensures that the chain makes no noise.

The rods 18, 21 are riveted on a U-shaped link of the chain 31 and aresecured with the other end to the inner member and the outer member,respectively, of the column by means of a pair of flaps 40. The flapsare inserted through a hole in an end plate in the members and aretwisted about the longitudinal axis for attachment.

It is observed that the motor is secured to the stick-shaped element bya dovetail connection, said motor being provided with a front coverformed with a dovetail grove and a counterpart in the stick-shapedelement, which is a simple configuration easy to mount.

For lateral guiding and positioning, the lower end of the stick-shapedelement is provided with a boss 41 on each side which is supportedagainst the inner side of the central profile when the drive device isinserted into it.

The term lifting column has been used in the foregoing, but it will beappreciated that the invention also covers linear actuators. A liftingcolumn is fundamentally a linear actuator arranged vertically.

1. A lifting column comprising first and second mutually telescopicallyslidable members and a drive device therefor, said drive devicecomprising a stick-shaped element which mounts first and second chainwheels at opposite ends thereof, said first chain wheel including ashaft, an endless first chain running over and between said first andsecond chain wheels to define a first chain run and a second chain runbetween the two chain wheels, said stick-shaped element at least in partextending between said first and second chain runs, an electric motorand a transmission mounted on the stick-shaped element, saidtransmission being directly connected to said electric motor and to saidfirst chain wheel, separately from said endless first chain, to drivesaid first chain wheel and thus move said endless first chain along saidfirst and second chain runs, and first connection means attached to saidchain along said first chain run for moving one of said first and secondslidable members, said electric motor being directly mounted on saidstick-shaped element and fixedly positioned relative to saidstick-shaped element.
 2. A lifting column according to claim 1, whereinthe stick-shaped element comprises two halves which may be assembledabout a longitudinal plane.
 3. A lifting column according to claim 1,wherein, in an area up to the motor, the stick-shaped element is formedwith a recess for the transmission or a part thereof as well as for thefirst chain wheel.
 4. A lifting column according to claim 1, wherein atleast the second chain wheel most remote from the motor is mounted on asubelement of the stick-shaped element and is secured longitudinallyslidably for tightening the chain.
 5. A lifting column according toclaim 1, wherein the transmission comprises a planetary gear having atoothed rim with an internal toothing in engagement with a planet wheel,which is in turn in engagement with a sun wheel, said toothed rim beingexternally configured as the first chain wheel.
 6. A lifting columnaccording to claim 5, wherein the stick-shaped element is locallyconfigured as a housing for the planetary gear.
 7. A lifting columnaccording to claim 5, wherein the transmission additionally comprises aworm drive, wherein the motor shaft is formed with the worm.
 8. Alifting column according to claim 7, wherein the worm drive and theplanetary gear are connected with a second chain drive, said worm wheelbeing connected with a third chain wheel and the sun wheel with a fourthchain wheel.
 9. A lifting column according to claim 8, including a chaintightener having at least one spring-loaded block, one end of the blockbeing intended for engagement with the first chain, the other end havinga snap locking part intended for cooperation with a boss for retentionof the block against spring action, said block being caused to engagethe first chain by the spring force when the snap locking part isreleased.
 10. A lifting column according to claim 1, wherein the motoris secured to the stick-shaped element with a dovetail connection, saidmotor being provided with a front cover formed with a dovetail grooveand a counterpart in the stick-shaped element.
 11. A drive liftingcolumn according to claim 1, including a rotary potentiometer forabsolute positional determination of the extended position of the drivedevice, said potentiometer being arranged in a recess in thestick-shaped element and driven via a toothed wheel on the shaft and inengagement with the drive chain.
 12. A lifting column according to claim1, configured as a table leg for height-adjustable tables.
 13. A liftingcolumn according to claim 1, wherein said first connection meanscomprise a first rod.
 14. A drive device for moving a movable element,comprising a stick-shaped element which mounts first and second chainwheels at oprosite ends thereof, said first chain wheel including ashaft, an endless first chain running over and between said first andsecond chain wheels to define a first chain run and a second chain runbetween the two chain wheels, said stick-shaped element at least in partextending between said first and second chain runs, an electric motorand a transmission mounted on the stick-shaped element, saidtransmission being directly connected to said electric motor and to saidfirst chain wheel, separately from said endless first chain, to drivesaid first chain wheel and thus move said endless first chain along saidfirst and second chain runs, first connection means attached to saidchain along said first chain run for moving a first movable element,said electric motor being directly mounted on said stick-shaped elementand fixedly positioned relative to said stick-shaped element, whereinsaid first connection means comprised a first rod, and including asecond means connected to said second chain run to move a second movableelement, said second means comprising a second rod.
 15. A drive deviceaccording to claim 14, wherein said first and second movable elementsare telescopic profiles.
 16. A drive device according to claim 14,wherein at least one electrical wire leading to/from the drive unit isconnected to one of the first and second rods.
 17. A drive deviceaccording to claim 16, wherein the stick-shaped element has a cavity forreceiving a length of said at least one wire in excess at any time,depending on an extended position of the drive unit.
 18. A drive deviceaccording to claim 14, wherein end stop positions are determined by twoend stop switches mounted on a common printed circuit board which may beinserted into a slot in the stick-shaped element.
 19. A drive deviceaccording to claim 18, wherein the first and second rods are providedwith means or are constructed themselves for activation of the end stopswitches.
 20. A drive device according to claim 14, wherein said firstand second rods each have a U-shaped cross-section which, with thesides, extends along the sides of the first chain.
 21. A drive deviceaccording to claim 20, wherein the side of one of the first and secondrods is formed with a longitudinal incision for the function key of theend stop switches so that in the positions between the end stops thefunction keys extend into the incision, while at the end stops the sideof the one rod will activate the respective end stop switch.
 22. A drivedevice according to claim 14, wherein a guide is provided on each end ofthe stick-shaped element for the respective first and second rods.
 23. Adrive device according to claim 14, wherein the second rod is guided ina lateral direction by a flange on the stick-shaped element.
 24. A drivedevice according to claim 20, wherein the first and second rods areriveted on a U-shaped link of the first chain.
 25. A drive deviceaccording to claim 20, wherein the outer end of the first and secondrods is formed with flaps for attachment in a structure in which thedrive device is to incorporated.
 26. A drive device for moving a movableelement, comprising a stick-shaped element which mounts first and secondchain wheels at opposite ends thereof, said first chain wheel includinga shaft, an endless first chain running over and between said first andsecond chain wheels to define a first chain run and a second chain runbetween the two chain wheels, said stick-shaped element at least in partextending between said first and second chain runs, an electric motorand a transmission mounted on the stick-shaped element, saidtransmission being directly connected to said electric motor and to saidfirst chain wheel, separately from said endless first chain, to drivesaid first chain wheel and thus move said endless first chain alone saidfirst and second chain runs, first connection means attached to saidchain along said first chain run for moving a first movable element,said electric motor being directly mounted on said stick-shaped elementand fixedly positioned relative to said stick-shaped element, andwherein at least one end of the stick-shaped element is provided with atleast a boss on each side as a lateral guide in a structure in which thedrive device is to be incorporated.